The present invention relates to thermographic recording materials whose prints have improved thermal development efficiency.
Thermal imaging or thermography is a recording process wherein images are generated by the use of thermal energy. In direct thermal thermography a visible image pattern is formed by image-wise heating of a recording material.
EP-A 903 625 discloses a substantially light-insensitive black and white monosheet thermographic recording material is provided comprising a support and a thermosensitive element containing a substantially light-insensitive organic silver salt, a 1,2-dihydroxyphenyl-compound in thermal working relationship therewith and a binder, characterized in that the 1,2-dihydroxyphenyl-compound is represented by formula (I): 
where R is xe2x80x94P(xe2x95x90O)R1R2, xe2x80x94SOxR3, xe2x80x94CN, xe2x80x94NO2 or xe2x80x94CR4xe2x95x90NR5 when n is 0; R is xe2x80x94P(xe2x95x90O)R1R2, xe2x80x94SOxR3, xe2x80x94CN, xe2x80x94NO2, xe2x80x94CR4xe2x95x90NR5 or xe2x80x94COR6 when n is a integer; R1 and R2 are independently an alkyl, a substituted alkyl, an aryl, a substituted aryl group, an alkoxy, a substituted alkoxy, an aryloxy, a substituted aryloxy, a hydroxy group, an amino group or a substituted amino group; R3 is an alkyl, a substituted alkyl, an aryl, a substituted aryl, an amino or a substituted amino group; R4is an alkyl, a substituted alkyl, an aryl or a substituted aryl group or hydrogen; R5 is an alkyl, a substituted alkyl, an aryl, a substituted aryl, a hydroxy, an alkoxy, an aryloxy, an acyl, an amino or a substituted amino group; R6 is an alkyl, a substituted alkyl, an aryl, a substituted aryl, an alkoxy, a substituted alkoxy, an aryloxy, a substituted aryloxy, a hydroxy, an amino or a substituted amino group or hydrogen; x is 1, 2 or 3; and the benzene ring of the 1,2-dihydroxyphenyl-compound represented by the formula (I) may be further substituted.
EP-A 978 760 discloses a substantially light-insensitive black and white monosheet thermographic recording material comprising a support and a thermosensitive element containing a substantially light-insensitive organic silver salt, a 1,2-dihydroxyphenyl-compound in thermal working relationship therewith and a binder, characterized in that the 1,2-dihydroxyphenyl-compound is represented by formula (I): 
where n is 0 or 1; R is xe2x80x94(Cxe2x95x90O)R1, xe2x80x94(Cxe2x95x90O)NR1R2, xe2x80x94CN, xe2x80x94SO3R2, xe2x80x94SO2R2, xe2x80x94SOR2, xe2x80x94SO2NR2R3 or xe2x80x94PO3R2R3; R1 is H or a substituted or unsubstituted alkyl group with 12 or less carbon atoms; and R2 and R3 are independently H or an alkyl, a substituted alkyl, an aryl or a substituted aryl group; and R1 and R2 together can provide the atoms to close a carbocyclic or heterocyclic ring; and R2 and R3 together can represent the atoms to close a carbocyclic or heterocyclic ring
Prior art thermographic recording materials whose prints exhibit acceptable archivability exhibit unsatisfactory Dmax/(silver behenate) coverage ratios i.e. the quantity of silver behenate required to obtain a given Dmax is too high. A means is needed to increase the Dmax/(silver behenate) coverage ratio without deterioration in print archivability.
It is therefore an aspect of the present invention to provide improved reducing agents for substantially light-insensitive black and white thermographic recording materials with improved thermal development efficiency i.e. improved Dmax/(organic silver salt coverage) ratios without significant deterioration in archivability of the prints obtained therewith.
Further aspects and advantages of the invention will become apparent from the description hereinafter.
Surprisingly it has been found that particular types of novel reducing agents produce an improvement in thermal development efficiency in thermographic recording materials as shown by an increase in the Dmax/(organic silver salt coverage) ratio without significant deterioration in archivability of the prints thereby obtained.
The above mentioned aspects are realized by providing a monosheet black and white substantially light-insensitive thermographic recording material comprising a thermosensitive element and a support, the thermosensitive element containing a substantially light-insensitive organic silver salt, a 1,2-dihydroxyphenyl-compound in thermal working relationship therewith is and a binder, wherein said 1,2-dihydroxyphenyl-compound is represented by formula (I): R1SO2R2, wherein R1 is an optionally substituted aryl group and R2 is selected from the group consisting of a 3,4,5-trihydroxyphenyl group, a 3-alkoxy-4,5-dihydroxyphenyl group and a 3-aryloxy-4,5-dihydroxyphenyl group; or said 1,2-dihydroxyphenyl-compound is represented by formula (II): R3COOR4, wherein R3 is a 3-alkoxy-4,5-dihydroxyphenyl group or a 3-aryloxy-4,5-dihydroxyphenyl group; and R is an alkyl group or an aryl group. Combinations of compounds according formula (I) or formula (II) may also be used that on heating become reactive partners in the reduction of the substantially light-insensitive organic silver salt.
The above mentioned aspects are also realized by providing a thermographic recording process for a monosheet black and white substantially light-insensitive thermographic recording material according to any of the preceding descriptions comprising the steps of: (i) providing the thermographic recording material; (ii) bringing the thermographic recording material into the proximity of a heat source; (iii) applying heat imagewise from the heat source to the thermographic recording material; and (iv) removing the thermographic recording material from the proximity of the heat source.
Several embodiments are disclosed in the description set forth herein.